Variations and asymmetry in the arteries that supply blood to the brain may be one of the key reasons behind why people get migraines, says new research.

The arteries that supply blood to the brain are connected via a ring of connections known as the circle of Willis. New research from the University of Pennsylvania indicates that in people who suffer from migraines, especially migraines with aura, the circle of Willis is more likely to be incomplete than with the rest of the population.

Previously, it was believed that migraines were caused by dilation of blood vessels in the brain. More recently, it has been attributed to abnormal neuronal signals. The new research however, indicates that abnormal blood vessel structures may increase susceptibility to changes in cerebral blood flow, which then causes the abnormal neuronal activity.

“People with migraine actually have differences in the structure of their blood vessels. This is something you are born with,” said Brett Cucchiara, lead author of the study, “These differences seem to be associated with changes in blood flow in the brain, and it’s possible that these changes may trigger migraine, which may explain why some people, for instance, notice that dehydration triggers their headaches.”

This is where the circle of Willis sits

The researchers have said that since both migraines and an incomplete circle of Willis are common, the association is likely only one of many causes for the affliction. They suggest that in the future however, one could diagnostically test the integrity of the circle, and thus help personalize migraine treatment.